In one prior-art separating grid of the kind outlined above, the collection and removal means of the fixed and mobile separating grid bars have a step-like configuration along the entire length of the bars, and the mobile separating grid bars are arranged to be actuated by a drive unit imparting to the mobile separating grid bars a closed path of movement in the plane of the grid bars, the vertical component of movement of which somewhat exceeds the height of the steps of the fixed grid bars.
In the prior-art separating grid, the mobile separating grid bars thus have a parallel displacement pattern similar to that of a draw-bar, i.e. all parts of the grid bars follow an identical circular path.
Because the lower ends of the mobile grid bars move vertically upwards and downwards to the same extent as forwards and backwards, it is very difficult to provide efficient sealing at the lower ends, particularly if one wishes to build a machine wherein the inter-bar spacing is smaller than the thickness of the separating grid bars. On account of the comparatively high velocity of the running water, solid particles and objects therefore will penetrate into the gaps between the fixed grid bars, which bars are left exposed as the lower ends of the mobile grid bars move vertically upwards with respect to said gaps.
The particles and objects that will fall through the grid entirely will be entrained by the running water, resulting in incomplete separation, with the result that further cleaning of the water will be required and/or that problems will be encountered in subsequent water-cleaning steps, with ensuing increase of costs and work.
The particles and objects that are so large, heavy, and/or hard that they are caught in the gaps between the fixed separating grid bars are hit by the lower edges of the mobile bars as the latter descend vertically into said gaps. The result is that these particles and objects, already stuck, will be forced further down into the gaps and finally clog the latter to a smaller or larger extent, or else, before this happens, the lower ends of the mobile grid bars may already have been deformed or made inoperative. Even if an increase of the grid bar dimensions were to make the bars more apt to withstand the stress to which they are exposed, the resistance would sooner or later reach such levels that the drive unit would no longer be capable of driving the mobile grid bars and come to a standstill, unless overload on the unit has already damaged it.
Irrespective of whether the mobile grid bars and the drive unit including the motion transmission mechanism associated therewith were to support the stress, the gaps between the fixed grid bars must be cleaned manually or with the aid of special equipment, of stuck or jamming particles and objects. This is a tedious and work-consuming job, in addition causing a more or less lengthy and serious shut-down. The situation is further aggravated if the grid bars or other components are damaged to such an extent that repairs and/or replacement of parts become necessary.